A steep rent rise is squeezing out the last of the Causeway Bay old-timers.

Kay Kwong-nam, 74, has sold traditional food and hairy crabs in the heart of the district for 29 years. His shop, Old San Yang, is on the corner of Lee Garden Road and Russell Street in the middle of the busy pedestrian link between Times Square and the Sogo department store.

The shop has been a tenant in the neighbourhood longer than any other. Sandwiched between a currency exchange and the skincare chain Origins, Old San Yang stands out: it is not a chain outlet and has no luxury goods in its windows.

But it must make way for a store selling European watches in April and move to the quieter Pak Sha Road nearby. Between them, Old San Yang and two neighbours pay less than HK$800,000 in rent. But all three must leave; the watch seller has promised to pay HK$1.43 million a month. Kay's rent is HK$350,000; to stay, he would need to pay at least HK$500,000 - 42 per cent more.

'The high rent is too much pressure for me,' he said. 'Even Li Ka-shing could not afford to run a loss-making business.'

The new tenant will pay the city's second-highest rent on a per square foot basis: HK$2,040. This is a world of commerce entirely removed from the one in which Kay, born in Zhejiang and brought to Hong Kong when he was six, was raised.

His family pioneered the introduction of traditional food from southern China and Shanghai to Hong Kong. His father started a grocery shop and brought a preserved salty soya bean sauce - best known for its use in stewing pork hock - to the city.

'I introduced Kam Wah dried ham to Chinese restaurants, and they love using it in shark's fin soup,' Kay said.

Better known to shoppers are the shop's hairy crabs. Kay has sold them for decades. It was always an expensive commodity because the crabs frequently died, Kay said. 'We used to send them to Hong Kong by train ... when they reached here, only one or two in a whole basket of them survived. Or they could all have died,' he said. The fatality rate dropped when he switched to air freight.

Kay opened his first shop in Hung Hom 40 years ago and moved to Causeway Bay a decade later, paying HK$92,000 in rent. 'A tram depot stood where Times Square is today,' he said. 'Many dai pai dong were in Russell Street, and it was so dirty that its nickname was 'rat street'.'

His shop served well-off people from Mid-Levels as well as nearby residents, many of them born in Shanghai or other parts of the mainland. Gradually those groups were replaced by mainland tourists.

'There were many Shanghainese along Paterson Street in Causeway Bay, and many in North Point too. North Point was nicknamed 'Little Shanghai'... most have moved away, but they still come back to my shop,' he said.

Among the shoppers were officials and celebrities. '[Former chief executive] Tung Chee-hwa came here twice, and [chief secretary] Henry Tang Ying-yen came here once. When Anson Chan Fang On-sang served as chief secretary, bodyguards accompanied her when she shopped,' he said.

Yet reputation alone could not help Old San Yang stay on the street, not with record high rents displacing old shops in Causeway Bay.

'I can do nothing but move,' Kay said. 'Only shops selling jewellery and watches can survive here, because they can earn enough to pay their bills with a few transactions a day.'